Silicon wafers are chemically etched to form semiconductor circuits. As part of the etching process a chemical typically referred to as photoresist is uniformly applied to the surface of the silicon wafer. A mask is then interposed between the silicon wafer and an energy source such as a light projector. The energy source is applied through the mask and exposes the photoresist. The photoresist is then dissolved with developers, leaving a pattern which is used to etch an image upon the silicon wafer.
Typically, photoresist is applied to the silicon wafer through a nozzle located at the center of the wafer. The wafer is rotated and centrifugal force distributes the photoresist along the surface of the wafer. Photoresist is expensive and it is therefore desirable to avoid applying more photoresist to a wafer surface than is required to properly coat the surface.